Changes in hydrocarbon emulsification specificity of the polymeric bioemulsifier emulsan: effects of alkanols

The biopolymer emulsan, which forms stable emulsions with mixtures of aliphatic and cyclic (or aromatic) hydrocarbons in water, does not emulsify aliphatic hydrocarbons alone [1-4]. Monohydric primary alcohols from hexanol to dodecanol were shown to enhance the formation of pure aliphatic hydrocarbon/water emulsions under conditions of mild agitation. Enhancement was a function of emulsan concentration and was proportional to alkanol concentration (5×10^-5 M to 2.5x10^-4 M) at constant bioemulsifier concentration (0.05 mg/ml). Enhancement of emulsification was also found when aqueous solutions of diethanolamine and phenethyl alcohol (5 to 30×10^-3 M) were substituted for the primary alcohols. None of these substances emulsified hexadecane or other n-alkanes in the absence of the biopolymer. The strongest enhancement of emulsification (3-fold) was observed with tetra- and hexadecane. At alkanol concentrations optimal for enhancement of emulsification, no significant lowering of hexadecane/ emulsan/water interfacial tension was observed. The possibility of a direct association of alkanols with the emulsan in solution, resulting in altered conformation of biopolymer and modification of its specificity toward hydrocarbons, is discussed.